Studies on chemiluminescence in the enzymatic and autoxidative transformation of 3,4-dihydroxyphenylalanine into eumelanins

The catechol oxidase-catalysed and autoxidative transformation of 3,4-dihydroxyphenylalanine (DOPA) to eumelanin have been studied by oxygen consumption, energy transfer, absorption and fluorescence spectroscopy. Formation of transient dopachrome (λ_max = 480 nm) and dopalutin (λ_ex = 423 nm, λ_em = 491 nm) have been found in the enzymatic and autoxidative reaction. In the enzymatic reaction, neither a photon emission with quantum yield Φ > 10^?13 nor energy transfer to triplet and singlet energy acceptors (sensitizers such as anthracene derivatives, xanthene dyes and chlorophyll-a) in water and micellar solutions have been found. The autoxidative reaction is chemiluminescent (Φ = 10^?9), the emission occurring in the 400-600 nm range. The excitation energy is not transferred to sensitizers. The effect of various enzymes and traps of active oxygen species as well as the spectral distribution of chemiluminescence indicate that there is no emission from oxygen dimoles. Carbonates and active species of oxygen are shown to participate in the chemiexcitation reaction.     

Determination of amine oxidases in tissues by peroxidation-induced chemiluminescence of phthalazines

A method is proposed for the determination of the activity of amine oxidases in purified samples and tissue homogenates. The method is based on the chemiluminescence of luminol and other cyclic hydrazides elicited by the horseradish peroxidase-catalyzed peroxidation using H₂O₂ produced in the amine oxidase reaction. Several aspects of the chemiluminescence method for determining enzymatic activity in crude tissue extracts are discussed.     

Chemiluminescence of lucigenin by electrogenerated superoxide ions in aqueous solutions

The chemiluminescence reaction of lucigenin (Luc²⁺?2NO₃^?, N,N′‐dimethyl‐9,9′‐biacridinium dinitrate) at gold electrodes in dioxygen‐saturated alkaline aqueous solutions (pH 10) was investigated in detail by the use of electrochemical emission spectroscopy. We noted that both O₂ and Luc²⁺ are reduced on a gold electrode in aqueous solution of pH 10 in almost the same potential region. From this fact, we expected chemiluminescence based on a radical–radical coupling reaction of superoxide ion (O₂·^?) and one‐electron reduced form of Luc²⁺ (Luc·⁺, a radical cation). Chemiluminescence was actually observed in the potential range where O₂ and Luc²⁺ were simultaneously reduced at the electrodes. The effects were examined upon addition of enzymes, i.e. superoxide dismutase (SOD) and catalase, into the solution and the substitution of heavy water (D₂O) for light water (H₂O) as a solvent on the chemiluminescence. In the presence of native and active SOD, chemiluminescence was completely absent. On the other hand, chemiluminescence was observed, unchanged in the presence of either denatured and inert SOD or catalase. In addition, the amount of chemiluminescence in D₂O solution was about three times greater than that in H₂O solution. These results, together with cyclic voltammetric results, suggest that O₂·^? participates directly in the chemiluminescence but H₂O₂ does not, and the chemiluminescence results from the coupling reaction between O₂·^? and Luc^·+ under the present experimental conditions. These chemically unstable species, O₂·^? and Luc·⁺, are produced during the simultaneous electroreduction of O₂ and Luc²⁺. The coupling reaction between those radical species would lead to the formation of a dioxetane‐type intermediate and, finally, to chemiluminescence. The chemiluminescence reaction mechanism is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

STUDIES ON NITRIC OXIDE FREE RADICALS GENERATED FROM POLYMORPHONUCLEAR LEUKOCYTES (PMN) STIMULATED BY PHORBOL MYRISTATE ACETATE (PMA)

The interaction of NO and O^?₂free radicals generated from PMA (phorbol myristate acetate)-stimulated PMN (polymorphonuclear leukocytes) was studied by a nitroxide spin trap, DMPO (5,5-dimethyl-1-pyrroline-1-oxide). It was found that addition of L-arginine to the system would significantly decrease the trapped O^?₂by DMPO and addition of N^G-monomethyl-arginine (NGMA) would significantly increase the trapped O^?₂by DMPO. It was proved that the formation of ONOO^?by the reaction of NO and O^?₂was the main reason for the decrease of trapped O^?₂in the experiment with xanthine/xanthine oxidase and irradiation of riboflavin systems. The yield of NO during this process was calculated. The generation dynamic of NO was studied by a luminol-dependent chemiluminescence technique and it was found that after stimulation of PMN by PMA, there would be an immediate, significant chemi-luminescence, which came mainly from the active oxygen free radicals generated by PMN. If L-arginine was added to this system, the chemiluminescence would increase about 100-fold, but NGMA inhibited the increase of the chemiluminescence. Ten minutes after addition of L-arginine, this increase did not change, the chemiluminescence peak decreased gradually, but the half life increased. The ESR and chemiluminescence properties of NO and ONOO^?synthesized were also studied in model systems.     

Redox Changes in Perfusates Following Intracerebral Penetration of Microdialysis Probes

Microdialysis probe insertion into rat cerebral cortex significantly affects the levels of redox-active substances in brain extracellular fluid. Ascorbic acid levels are high immediately after probe insertion, decline rapidly, and then rise as the rat recovers from anesthesia 5–8 hours after surgery. Uric acid is at a low level for 5 hours and then rapidly increases in parallel with ascorbic acid. High ascorbic acid levels immediately after probe insertion are likely due to a shift from intracellular to extracellular fluids, whereas the delayed increase in uric acid may be due to increased enzymatic formation. After removal from the brain, hydrogen peroxide (H₂O₂) in microdialysis samples produces catalase-sensitive oxidative chemiluminescence. Microdialysis samples also produce high level catalase-resistant chemiluminescence associated with ascorbic acid levels after penetration injury. Although ascorbic acid is likely an antioxidant at concentrations estimated to be in brain extracellular fluid, it may have prooxidant effects when complexed with transition metals released into the neuronal microenvironment during traumatic brain injury.     

A continuous spectrophotometric assay for determination of the aureusidin synthase activity of tyrosinase

Introduction – Aurones (aureusidin glycosides) are plant flavonoids that provide yellow colour to the flowers of some ornamental plants. In this study we analyse the capacity of tyrosinase to catalyse the synthesis of aureusidin by tyrosinase from the chalcone THC (2′,4′,6′,4–tetrahydroxychalcone). Objective – To develop a simple continuous spectrophotometric assay for the analysis of the spectrophotometric and kinetic characteristics of THC oxidation by tyrosinase. Methodology – THC oxidation was routinely assayed by measuring the increase in absorbance at 415 nm vs. reaction time. Results – According to the mechanism proposed for tyrosinase, the enzymatic reaction involves the o‐hydroxylation of the monophenol THC to the o‐diphenol (PHC, 2′,4′,6′,3,4 – pentahydroxychalcone), which is then oxidised to the corresponding o‐quinone in a second enzymatic step. This product is highly unstable and thus undergoes a series of fast chemical reactions to produce aureusidin. In these experimental conditions, the optimum pH for THC oxidation is 4.5. The progress curves obtained for THC oxidation showed the appearance of a lag period. The following kinetic parameters were also determined: K_m = 0.12 mM, V_m = 13 μM/min, V_m/K_m = 0.11/min. Conclusion – This method has made it possible to analyse the spectrophotometric and kinetic characteristics of THC by tyrosinase. This procedure has the advantages of a short analysis time, straightforward measurement techniques and reproducibility. In addition, it also allows the study of tyrosinase inhibitors, such as tropolone. Copyright © 2009 John Wiley & Sons, Ltd.     

Light generation with Fenton's reagent its relationship to granulocyte chemiluminescence

A simple chemical system consisting of FeSO₄ and H₂O₂ (Fenton's reagent) was shown to emit light (chemiluminescence). The addition of tryptophan to the reaction markedly enhanced light production. Very little chemiluminescence was observed when H₂O₂ was omitted from the reaction and when ferric, instead of ferrous, ions were used. Hydroxyl radical (OH^.) and singlet oxygen (¹Δ_gO₂) quenchers suppressed chemiluminescence of the FeSO₄ + tryptophan + H₂O₂ system; and, deuterium oxide (²H₂O) enhanced chemiluminescence of both FeSO₄ reactions. These observations suggest that a radical chain reaction involving both OH^. and ¹Δ_gO₂ is responsible for the chemiluminescent reactions. Six iron-containing proteins, some of which are located within granulocytes, all emitted light in the presence of H₂O₂. Since iron and H₂O₂ are present in metabolically stimulated granulocytes, it is likely that chemiluminescent reactions similar to the ones demonstrated in this study account for part of the chemiluminescence of activated granulocytes.     

Determination of absolute chemiluminescence quantum yields for reactions of bis-(pentachlorophenyl) oxalate,hydrogen peroxide and fluorescent compounds

Absolute chemiluminescence quantum yields (?_CL) for reactions of bis-(pentachlorophenyl) oxalate (PCPO), hydrogen peroxide (H₂O₂) and 9:10 diphenyl anthracene (DPA) have been determined. A fully corrected chemiluminescence monitoring spectrometer was calibrated for spectral sensitivity using the chemiluminescence of the bis-(pentachlorophenyl) oxalate system as a liquid light source, the total photon output of which had previously been determined by chemical actinometry. At high (PCPO)/(H₂O₂) ratios ?_CL was found to be independent of PCPO and H₂O₂ concentrations.     

Interaction of trout hemoglobin with H2O2: a chemiluminescence study

Erythrocytes from trout Salmo irideus are characterized by four different hemoglobin components (HbI, HbII, HbIII and HbIV), HbI and HbIV being predominant. In this study we describe the interaction between trout hemoglobin (HbI and HbIV) and H₂O₂ using a chemiluminescence assay. Our data show that the reaction of hemoglobins with H₂O₂ produces a time-limited and significant increase of chemiluminescence signal. The half-life of the decay of this chemiluminescence signal was characteristic for each type of hemoglobin used. These results indicate the formation of excited molecules related to the interaction between trout hemoglobin and H₂O₂. © 1997 John Wiley & Sons, Ltd.     

Avicel hydrolysis by cellulase enzyme in supercritical CO2

Summary The enzymatic hydrolysis reaction in supercritical CO₂ to produce glucose from cellulosic material Avicel was investigated. In comparison with the result from the enzymatic hydrolysis reaction of Avicel without CO₂ introduced as a reaction medium, the reaction rate and glucose concentration are increased.     

Moderate O3/O2 therapy enhances enzymatic and non-enzymatic antioxidant in brain and cochlear that protects noise-induced hearing loss

Mitochondrial damage and oxidative stress are known to contribute to the pathogenesis of noise-induced hearing loss (NIHL). In this study, we examined the protective effect of O₂/O₃ mixture (ozone/oxygen) therapy against mitochondrial induced damage and oxidative stress by noise exposure in rat brain and cochlear. For this purpose, rats were divided into four groups: 1 – control group; 2 – noise-exposed group (100?dB); 3 – noise?+?O₂/O₃, and 4 – O₂/O₃ (30 µg/ml). After 14 d, animals were anesthetised. Rat brain and cochlear tissue were removed for evaluation of the histopathological damages, oxidative stress, and mitochondrial dysfunction in both tissues. Our findings indicated that noise caused pathological damage, oxidative stress, and mitochondrial dysfunction in rat brain and cochlear. Also, daily administration of an O₂/O₃ therapy (30 µg/ml intravenous) efficiently increased enzymatic and non-enzymatic antioxidant in brain and cochlear that this action led to inhibition of pathological damages, oxidative stress, reactive oxygen species formation, mitochondrial membrane potential (MMP) collapse, mitochondrial swelling, and cytochrome c release resulting from noise. These findings suggest that the moderate O₂/O₃ therapy enhances the capacity of enzymatic and non-enzymatic antioxidant in brain and cochlear that protects against NIHL.     

Evaluation of droplet-based microfluidic platforms as a convenient tool for lipases and esterases assays

Abstract

The accurate estimation of kinetic parameters is of fundamental importance for biochemical studies for research and industry. In this paper, we demonstrate the application of a modular microfluidic system for execution of enzyme assays that allow determining the kinetic parameters of the enzymatic reactions such as V_max – the maximum rate of reaction and K_M – the Michaelis constant. For experiments, the fluorogenic carbonate as a probe for a rapid determination of the kinetic parameters of hydrolases, such as lipases and esterases, was used. The microfluidic system together with the method described yields the kinetic constants calculated from the concentration of enzymatic product changes via a Michaelis–Menten model using the Lambert function W(x). This modular microfluidic system was validated on three selected enzymes (hydrolases).     

The photooxidation of glyoxylate by envelope-free spinach chloroplasts and its relation to photorespiration

Large quantities of CO₂ are released within many photosynthesizing tissues in the light by the process of photorespiration. This CO₂ arises largely from the carboxylcarbon atom of glycolate, which is synthesized in chloroplasts during photosynthesis. Glyoxylate is then produced by the glycolate oxidase reaction. The glyoxylate may be directly decarboxylated to CO₂, but some investigators believe the glyoxylate must first be converted to glycine before CO₂ is released during photorespiration. Spinach chloroplasts with their envelope membranes removed in dilute buffer solution have now been shown to carry out the oxidative decarboxylation of [1-¹⁴C]glyoxylate, in the presence of light and manganous ions in an atmosphere containing oxygen, to yield 1 mole each of ¹⁴CO₂ and formate. Rates of enzymatic decarboxylation exceeding 50 μmoles of ¹⁴CO₂ mg chlorophyll⁻¹ hr⁻¹ were obtained at pH 7.6; hydrogen peroxide is probably the oxidant in the reaction. Heated chloroplasts are inactive under the standard conditions and there is an almost absolute requirement for each of the components listed above. Conditions for some other nonenzymatic decarboxylations of glyoxylate have also been described. [1-¹⁴C]Glycine is decarboxylated by the enzymatic system at only 1% of the rate of [1-¹⁴C]glyoxylate. Maize chloroplast preparations are much less active than spinach chloroplasts. The high rates of CO₂ produced by the spinach system directly from glyoxylate, as well as the need for light and oxygen, suggest that this reaction functions in photorespiration, and that CO₂ arises during photorespiration without glycine as a mandatory intermediate.     

What do we measure with luminol-, lucigenin- and penicillin-amplified chemiluminescence? 1. Investigations with hydrogen peroxide and sodium hypochlorite

Evidence is provided that the amplifiers luminol and lucigenin react with different reactive oxygen species (ROS), depending on the ROS-generating system used. H₂O₂ is used to produce calibration curves for luminol- and lucigenin-amplified chemiluminescence. With this chemiluminescence generator we characterized the specificity and sensitivity of luminol- and lucigenin-amplified chemiluminescence and also studied penicillin G, a known enhancer of luminol-amplified chemiluminescence. The combination of luminol and lucigenin in reciprocally changing concentrations is effective in an additive manner, but the weak amplifier penicillin increases luminol-amplified chemiluminescence distinctly more than in an additive manner in different combinations. Lucigenin-amplified chemiluminescence is increased by penicillin at about 1% of the optimum concentration of penicillin; increasing concentrations of penicillin are less and less effective. On the other hand, low lucigenin concentrations enhance penicillin-amplified chemiluminescence at optimum penicillin concentrations more than in an additive manner. Fe²⁺ does not alter luminol-, lucigenin- or penicillin-amplified chemiluminescence. Co²⁺ increases luminol-amplified chemiluminescence by a factor of 100. Lucigenin- and penicillin-amplified chemiluminescence are minimally enhanced by Co²⁺. Cu²⁺ enhances luminol-amplified chemiluminescence with increasing concentrations by a factor of 1000. Lucigenin-amplified chemiluminescence increases also by the factor of 1000, but the concentration–reaction curve is not as steep. NaOCl enhances H₂O₂/Fe²⁺-driven luminol-amplified chemiluminescence in a concentration-dependent manner by a factor of 10⁴ (in the highest concentration of 10 mmol/L) and lucigenin amplified chemiluminescence only by a factor of about 25. Catalase (CAT) abolishes luminol-, lucigenin- and penicillin-amplified chemiluminescence completely, whereas superoxide dismutase (SOD) has no effect on luminol- or penicillin-amplified chemiluminescence, but enhances lucigenin-amplified chemiluminescence five-fold increasingly with increasing SOD activity. © 1998 John Wiley & Sons, Ltd.     

Starch hydrolysis using enzyme in supercritical carbon dioxide

Summary The enzymatic hydrolysis reaction with supercritical carbon dioxide(SC-CO₂) as a reaction medium to make glucose from starch was investigated. The reaction rate was enhanced at higher temperature and pressure, especially near the critical point of the CO₂. The -amylase and glucoamylase were found to be active in a SC-CO₂.     

Determination of free cholesterol based on a novel flow‐injection chemiluminescence method by immobilizing enzyme

A novel flow injection chemiluminescence method is proposed for determination of cholesterol in this paper. The cholesterol oxidase was immobilized onto sol–gel and prepared as an enzymatic reaction column. The determination of cholesterol was performed by quantitative determination of hydrogen peroxide produced from an enzymatic reaction. The luminol–H₂O₂–metal chelate diperiodatocuprate(III) system ensured that the method was highly sensitive and selective. Free cholesterol was determined over the range 5.0 × 10^–8 mol/L–5.0 × 10^–7 mol/L, with a limit of detection (3σ) of 1.9 × 10^–8 mol/L. The relative standard deviation (RSD) for 2.5 × 10^–7 mol/L was 2.7% (n = 7). The proposed method offered the advantages of sensitivity, selectivity, simplicity and rapidity for free cholesterol determination, and was successfully applied to the direct determination of free cholesterol in serum. Copyright © 2008 John Wiley & Sons, Ltd.     

Chemiluminescence method based on the KIO4−K2CO3−Mn2+ reaction for rapid and sensitive determination of forchlorfenuron in dried fruit

Forchlorfenuron is a low-toxic phenylurea plant growth regulator. Excessive intake of forchlorfenuron can lead to metabolic disorders of the matrix and be harmful to human health. The chemiluminescence intensity of the KIO₄–K₂CO₃–Mn²⁺ reaction decreased in the presence of forchlorfenuron. Based on this result, a rapid and sensitive chemiluminescence method was established to determine forchlorfenuron by combining it with a batch injection static device. The injection speed, injection volume and reagent concentration of the forchlorfenuron–KIO₄–K₂CO₃–Mn²⁺ chemiluminescence reaction were optimized. Under these optimized conditions, the linear range of the method was 1.0–200.0 μg/L, and the limit of detection was 0.29 μg/L (S/N = 3). The chemiluminescence method for the determination of forchlorfenuron could be completed in 10 s. The method was applied to detect the residual forchlorfenuron in dried fruit samples, and the results are consistent with high-performance liquid chromatography-mass spectrometry. This method has the advantages of high sensitivity, rapid response, less reagent consumption, and convenient operation. It will provide a new perspective for chemiluminescence for the rapid and sensitive determination of forchlorfenuron in various complex samples.     

Chemiluminescent determination of esterases in monocytes

Esterase from monocytes promotes the hydrolysis of 2-methyl-1-propenylbenzoate (MPB) yielding 2-methyl-1-propenol, which is oxidized by horseradish peroxidase/H₂O₂ producing triplet acetone. The chemiluminescence of this reaction can be enhanced by the addition of 9,10-dibromoanthracene-2-sulphonate. The non-specific esterase present in monocytes is responsible for MPB hydrolysis, since (a) the chemiluminescence of the reaction was inhibited by fluoride, and (b) cells that do not contain a significant amount of non-specific esterases, e.g. lymphocytes and neutrophils, did not trigger light emission. The analytical application of this reaction is considered. © 1998 John Wiley & Sons, Ltd.     

Optimization of peroxynitrite–luminol chemiluminescence system for detecting peroxynitrite in cell culture solution exposed to carbon disulphide

We established a peroxynitrite–luminol chemiluminescence system for detecting peroxynitrite in cell culture solution exposed to carbon disulphide (CS₂). Three factors, including exposure time to ozone (Factor A), volume of peroxynitrite (ONOO^?) solution (Factor B) and luminol concentrations (Factor C) at three levels were selected and the combinations were in accordance with orthogonal design L₉ (3⁴). Peroxynitrite was generated from the reaction of ozone and 0.01 mol/L sodium azide (NaN₃) dissolved in carbonic acid buffer solution (pH 11), and it was reacted with luminol to yield chemiluminescence. The peak value, peak time and kinetic curve of the light emission were observed. The selected combination conditions were 50 s ozone, 800 µL peroxynitrite and 0.001 mol/L luminol solution. Cell culture solution with CS₂ enhanced the emission intensity of chemiluminescence (F = 8.38, p = 0.018) and shortened the peak time to chemiluminescence (F = 139.00, p = 0.0001). The data demonstrated that this luminol chemiluminescence system is suitable for detecting peroxynitrite in cell culture solutions for evaluating the effect of CS₂ on endothelial cells. Copyright © 2003 John Wiley & Sons, Ltd.     

FeS2 nanosheets–H2O2–NaHCO3 chemiluminescence method for procaine hydrochloride determination

FeS₂ nanosheets (NSs) were produced and exploited as a new catalyst for a chemiluminescence (CL) reaction. The characterization of FeS₂ NSs was performed using spectroscopic methods. In this regard, transmission electron microscopy images showed that FeS₂ NSs have a length of ~0.5–1 μm. The direct optical band gap energy of FeS₂ NSs was found to be 3.45 eV. Prepared FeS₂ NSs were used to catalyze the NaHCO₃–H₂O₂ CL reaction. It was found that procaine hydrochloride (PCH) could reduce the intensity of the FeS₂ NSs–NaHCO₃–H₂O₂ CL reaction so, with increasing PCH concentrations, the intensity of light emission decreased. Therefore, a simple and sensitive method was introduced to measure PCH with a linear range expanded from 1.00 × 10⁻⁶ to 1.00 × 10⁻³ mol L⁻¹ and an 8.32 × 10⁻⁷ mol L⁻¹ limit of detection. Studies related to the effect of foreign species and reaction mechanisms were performed. The application of the approach was verified by quantifying the PCH in the injection.